Piston Ring Cylinder Research Articles

Clarification of a Semi-Empirical Approach in Piston Ring-Cylinder Bore Conformability Prediction

This technical brief clarifies origins of the piston ring conformability bounds presented by Dunaevsky (1990, Tribol. Trans. 33(1), pp. 33–40) and provides their correct expression. The subject has strong practical significance in the field of piston engines and compressors, and it is currently getting additional prominence due to stringent emission regulations. The bounds stem from an earlier version, developed by the authors using a semi-empirical approach, and published in the 1970s in Russian technical journals. A semi-empirical background of the bounds was inadvertently missed in the aforementioned Tribology Transactions’ publication. This fact, and the virtual inaccessibility of Russian sources to the English reader, interfere with the proper use of the bounds and cloud their authorship. In this technical brief, the correct expression of these conformability bounds, the development process, and uses are highlighted.

Modeling of Abrasive Wear in a Piston Ring and Engine Cylinder Bore System©

Engine-related improvements such as more efficient engine components, improved engine oils, and high-performance coating materials, need to be verified in terms of their effects on the tribological performance of the piston ring/cylinder bore system. The main purpose of this research is to develop an abrasive wear model for the piston ring/cylinder bore system during steady-state operation by considering the effects of temperature, load, oil degradation, surface roughness, and material properties. The model can be used either in theoretical modeling or integrated with finite element analysis. Based on a laboratory simulator, a three-body abrasive wear model has been developed to model the wear progression of the piston ring/cylinder bore system during steady state operation. The proposed novel abrasive wear model addresses the effects of temperature, load, oil degradation, surface roughness, and material properties. The feasibility of the proposed model is illustrated by a numerical example.

Testing the tribological properties of lubricants and materials for the system “piston ring/cylinder liner” outside of engines

The test procedure for characterizing the tribological behavior of lubricants and materials for the system “piston ring/cylinder liner” outside of engines is now operational and validated. The test parameters presented in this paper (FN=50 N; v=0.3 m/s, s=24 km) may act only as an indicator and should be used to the tasks regarded. It allows the check prior expensive engine testing, if a tribomaterial, tribocouple or new lubricant will reach a satisfactory engine performance. The introduction of piston ring segments and cylinder liner as specimen into the test rig as well as the volumetric wear determined by means of stylus profilometry represented a big step forward in order to increase the transferability of “tribotests” to engine tests on an acceptable level.

Tribological characteristics and surface interaction between piston ring coatings and a blend of energy-conserving oils and ethanol fuels

The friction and wear performance of coatings on nitrided stainless steel (NSS) piston rings and chrome plated stainless steel rings sliding against cast iron cylinder liner segments in fully-formulated engine oils were investigated by using a high frequency reciprocating tribometer. The ring coatings include thermal-sprayed CrN and physical vapor deposited (PVD) diamond-like-carbon (DLC). The tribological characteristics of piston ring coatings were determined by applying several advanced piston ring coatings and energy-conserving lubricants containing friction modifiers. The impacts of E85 ethanol fuel (a fuel blend of 85% ethanol and 15% unleaded gasoline) on scuffing of the chrome-coated piston ring and cast iron cylinder liner segment were studied with different fuels varying in their degree of acidity. The tribological characteristics due to surface interactions between piston ring coatings and energy-conserving engine oils containing molybdenum dithiocarbamate (MoDTC) or an organic friction modifier were compared and analyzed. The test results show that the DLC coating produces the lowest wear on the cylinder liner segment and has a similar ring wear to nitrided and CrN coated piston rings. With MoDTC present in the engine oil, friction and wear are effectively reduced. The acidic fuel promotes the occurrence of scuffing.

Piston Ring-Cylinder Bore Friction Modeling in Mixed Lubrication Regime: Part I—Analytical Results

An axi-symmetric, hydrodynamic, mixed lubrication model has been developed using the averaged Reynolds equation and asperity contact approach in order to simulate frictional performance of piston ring and cylinder liner contact. The friction force between piston ring and cylinder bore is predicted considering rupture location, surface flow factors, surface roughness and metal-to-metal contact loading. A fully flooded inlet boundary condition and Reynolds boundary conditions for cavitation outlet zone are assumed. Reynolds boundary conditions have been modified for non-cavitation zones. The pressure distribution along the ring thickness and the lubricant film thickness are determined for each crank angle degree. Predicted friction force is presented for the first compression ring of a typical diesel engine as a function of crank angle position.

Piston Ring-Cylinder Bore Friction Modeling in Mixed Lubrication Regime: Part II—Correlation With Bench Test Data

A bench friction test system for piston ring and liner contact, which has high stroke length and large contact width has been used to verify the analytical mixed lubrication model presented in a companion paper (Part 1). This test system controls the speed, temperature and lubricant amount and records the friction force, loading force, crank angle signal and contact temperature data simultaneously. The effects of running speed, applied normal load, contact temperature and surface roughness on friction coefficient have been investigated for conventional cast-iron cylinder bores. Friction coefficient predictions are presented as a function of crank angle position and results are compared with bench test data. Analytical results correlated well with bench test results.

Scuffing failure analysis and experimental simulation of piston ring–cylinder liner

The scuffing failure phenomenon of piston ring–cylinder liner is studied theoretically and experimentally. The load and bulk temperature when scuffing failure occurs are measured under different engine speed, lubricant, and environmental temperature in a bench test. Based on the experimental results, the asperity capacity when scuffing occurs is evaluated. Surface contact temperature is determined with the measured bulk temperature and the surface flash temperature calculated by Blok theory. The scuffing failure threshold of piston ring–cylinder liner is established by using specific oil film thickness.

Technique for Experimental Evaluation of Piston Ring—Cylinder Film Thickness

A technique for estimating the piston ring film thickness by measuring the ring end gap has been developed. This paper discusses the details of the measurement technique, presents the results of a parametric study of the measured film thickness for unpressurized full-size diesel engine piston rings and compares those results with an analytical model. The film thickness is shown to depend upon the lubricant viscosity, the piston speed, the ring face profile and the quantity of lubricant available to the ring. The results of an analytical model, which assumes flooded lubrication conditions is also presented and the resulting film thicknesses are similar to those measured.

Radiotracer method for investigation of antiwear properties of lubricating oil additives under conditions of electro-erosive wear

An experimental unit has been designed to model the friction of a cylinder-piston ring block when applying constant voltage to the radioactive rubbing parts separated by a lube-oil layer. Wear was measured with a radiometric sealer and the readings recorded by an electronic potentiometer. It has been established that, at a constant voltage applied to the rubbing surfaces in the test unit, electro-erosive wear takes place. Extensive studies of antiwear properties of additives and mixtures of additives for motor oils have been carried out using this experimental unit. The method developed makes it possible to characterize not only the antiwear effect of the additives in the process of testing, but also the after-effect of these additives. It also enables additive mixtures to be formulated from selected components with due regard for synergism.